[Are there no other sieges beside Giran Castle?]

Newbie here, watched Giran siege the other day - a little boring (sporadic fights, nothing major), but I wondered about the other castles - there seems to be no other castles owned by anyone?

Is Giran the only castle siege for some reason?  I remember way back that all castles had sieges, and used to be massive fights.  The massive part I can sort of expect to be less now given less players, but seems odd no other castles can be sieged?

[Summoner Spell: Spirit Sharing - what does it actually do?]

It sounds like it gives me some buffs (e.g. P. Atk +4%), but it also says transfers master's enhanced skills to Servitor.  What skills?

It's a really hard spellbook to find (and one I saw was costly) - as a newbie I don't want to be spending all my adena if its not a good skill.

[Lineage 2 Classic - Where do you get an "Inventory Expansion Ticket Lv. 1"?]

I was wondering this too - I can't find lvl1, and lvl4 is in the L2 store (or is that the only one?)